The temperature-programmed desorption of oxygen from an alumina-supported silver catalyst

The associative desorption kinetics of O-2 from a 15 wt% Ag/alpha-Al2O3 catalyst were studied under atmospheric pressure in a microreactor set-up by performing temperature-programmed desorption (TPD) experiments. Saturation with chemisorbed atomic oxygen (O-*) was achieved by dosing O-2 for 1 h at 523 K and at atmospheric pressure followed by cooling in O-2 to room temperature. The TPD spectra showed almost symmetric O-2 peaks centred above 500 K, indicating associative desorption of O-2 from Ag metal surface sites. By varying the heating rates from 2 to 20 K min(-1), the O-2 TPD peak maxima were found to shift from 508 to 542 K, respectively. A microkinetic analysis of these TPD traces yielded an activation energy for desorption of 149 +/- 2 kJ mol(-1) and a corresponding pre-exponential factor of 2 x 10(12) +/- 1 x 10(12) s(-1) in good agreement with the kinetic parameters reported for O-2 desorption under UHV conditions from Ag(111) and Ag(110) single crystal surfaces.